Engineers: Help me understand the energy imparted to Massa's head

You must remember that when the spring fell off Barrichellos car, it was traveling the same speed as the rest of the car. FORWARD. The maximum speed it could have had towards Felipe's car was ZERO. If it was still flying around, its speed would have to be SUBTRACTED from the Ferrari's speed!

 

I would normally totally agree, but the object was a spring and could have had a different reaction than a solid object?

 

From the photos I have seen of poor Massa's superficial injuries his crash-helmet visor seems intact, penetration of the helmet itself having occurred just above and to the left of the visor opening. Massa's left eyelid up to the eyebrow was deeply gashed by some penetrating surface and presumably it is his left eyebrow and forehead area in which his primary skull fracture has occurred. We are also told that he has sustained a basal skull fracture, presumably due to his head being knocked back with the tremendous impact from the 800-gramme coil spring. One wonders what role his HANS device might have played during the micro-seconds of impact and rebound?

If the orbit of the poor guy's left eye has been displaced he faces a real recovery problem. When Stirling Moss's face was crushed in his 1962 Goodwood crash his cheekbone had to be rebuilt, which process changed the relative positioning of his eyes. This badly affected his previously fantastic depth perception, and it took several years before his brain taught itself to interpret visual inputs with anything approaching his native-born precision. I believe it's called diploplia? It is really bad news for a professional racing driver. Fingers crossed that this has not happened in Felipe's case.

DCN

 

A friend of mine who is an engineer said that the impact was equivallent to an Ak47 round.

 

yes. but from the pictures it appears the spring hit sideways (not the compressible axis of the spring) so the elasticity is negligible.

 

I thought a base fracture of the skull was caused by the velocity of the head in a high G impact and the spine becomming detached or fractured from the base of the skull. correct me If im wrong but that was my reason for suggesting the Hans Device didnt do its job fully?

 

No. Given the short timespan of the impact and the huge stiffness of springs in suspension use, it doesn't matter if it's a spring or not - even if it had hit im in its compression axis.

 

SpeedTv stated that the impact was around 1600 foot pounds. That is the same energy delivered by a 30-06.

 

Here is the testing procedures for Snell Memorial Foundation certification of a helmet

http://www.smf.org/testing.html

And a video of the impact testing

http://www.smf.org/video/snell_testing_wmv.html

 

Thanks for Snell link, I was lazy earlier. I think the 1600ft/lb # was purely made up. The 300G impact good, but penetration # lower than I'd expect, and he caught it at weak part of eye-opening/face shield.

Florian, I agree that the velocity would be zero towards car, it still had some vertical energy hence bounce. Looked like it was moving as closing speed was so high.

On replays, he was moving arms a bit, not agitated when he went into bus. Swelling and/or bleed could have been sudden, basilar skull fracture contre-coup maybe? Pure guesses at this point, but not a nice combination of events.

Doug, diplopia is correct, and if it was a blow-out fracture of orbit, it could be worse, could entrap/tear optic nerve.

Pray this comes out his way.

 

Completely agree.

I only did an example calc with specified assumptions to show the forces become huge when events occur in less than a millisecond...

as for accuracy... prob better than the US CBO (congessional budget office) , but as you say, meaningless in a scientific sense!

 

Well the velocity towards the car obviously wasn't zero, but we can safely assume that Massa's speed (relative to the track) was the major factor and thus the speed of the spring, in whichever direction, can be neglected... in the calculations that we don't do Just that everyone knows that the spring WASN'T in any way flying towards Massa, but Massa was travelling towards the spring...
(Edit: Which of course is meaningless for the damage done, the only thing matters is the relative speed)

The point about the short time spans is very true. With you and Sfumato being the professionals here: Is a short peak of high force worse for the head than the same amount of energy over a longer timespan (but stil in the millisecond range)?

 

In car camera http://globoesporte.globo.com/Esportes/Formula_1/Fotos/0,,GF73246-15011,00.html#fotogaleria=1

start and #1 and go thru #11

Carol

 

First, I have a BS in engineering and an MD. I'm a radiologist. Did 1 year surgery internship at a major trauma hosp (jackson memorial - miami). But by no means am I an expert in brain trauma...

In most situations high impulse (short time to peak) trauma is the most devastating to the brain tissue directly. bleeding, for example from skull fx, resulting in increased intracranial pressure can occur slowly, but still be devastating... but the brain is injured from the accumulating blood... but not the direct trauma (this is my understanding of natashia richardsons injury)

remember, the entire point of car crumble zones and F1 energy absorbing nose/tail cones is to spread the crash energy over a longer period of time, thus reducing the peak force / energy impulse.

I.e., same energy spread over a longer period...

 

Thanks Carol

G force of the scale ...brake and throttle..still on.
Image Unavailable, Please Login

 

Force is difficult to estimate, here.

F=ma means you'd have to calculate the acceleration time of the spring, between its speed on the track and the speed after impact -- neither of which we actually know.

Another estimate of force would be F = dE/dX -- the differential of energy over the distance applied, again containing unknowns.

The best I was able to come up with was a very rough kinetic energy estimate, based on about 275 kph difference between the car (helmet) and spring, and 0.8 kg mass: E = 0.5 m - v^2.

It worked out to about the same kinetic energy as an entire F1 car at 10 kph ... and having it hit you in the head at that speed.

But kinetic energy alone doesn't really say much. How bad the impact is would depend on the the amount of time over which how much kinetic energy transferred from the helmet to the spring.

The other factor to examine would be the deceleration when the car hit the tire barrier.
I don't know if they've done any studies on the operation of KERS when the driver is already unconscious.

 

Thanks Simon! The crumble zone thing etc is of course obvious (at least to me, but then again I'm studying that stuff!), what I specifically wonder about is if there's still a benefit of spreading the acceleration when the timespans are already very small. I guess it doesn't sound too clear what I'm talking about, I have a diagram somewhere which illustrates what I mean... with the emphasis on "somewhere"...

 

Another factor that we know nothing about: IIRC, the back of the helmet has contact to the chassis when the driver sits in the car (ie, like leaning your head against the headrest). Now when the spring hit the helmet, the "path" of the force was partly through the helmet "into" the chassis, meaning that Massa's head didn't have to take that load. There are just too many different variables involved to even hazard a guess on actual numbers...

Speaking of KERS and an unconscious driver, I think that doesn't matter too much. The driver not being conscious is already the worst "state" of the system "car and driver", I don't think it matters too much if there's another system involved in the powertrain or not.

 

That's what I meant--a spring should be decelerating quickly by releasing energy and wind resistance, rapidly gaining speed relative to Massa. Obviously that's what happened given the extend of the damage it caused. They said the spring weighed about two pounds, which is a sizable chunk of mass. From the replay you can see the spring is coming back up towards the car from the left, implying it had hit the ground and was bouncing back up.

My car was struck by a small piece of metal that came off a truck at highway speeds, 60-70 mph. The truck was in the next lane, the piece popped up into the air and hit the roofline of my car. The windshield was completely spidered and it left a huge dent in the roof.

 

Absoiuteley true! I just wanted to underline your observation with my post, was not meant to correct you, if it left that impression

 

But it does...

Peak force will be related to the inverse of time squared... double the time... decrease the peak force by a factor of 4.

if you can change an impact event that would have occurred in 1 mSec, and via a crumple zone spread it out over 5 mSec you decrease peak force by a factor of 25.

Thats why those silly little nose cones accomplish so much!

Same logic with a stunt man jumping off a building into a air bag.

 

Short intense spikes vs same force distributed even miniscularly broader are worse. Shear forces on vessels not intended to take huge G forces tear things, and brain still moving even when skull stops. Probably what caused a leak/bleed for IC hypertension.
BTW, I meant velocity was relatively zero/fractional/approaching zero. Mathematician in me shouldn't generalize

 

Arrgh. Acronym overload. My bad. (I was dashing that off before watching the Indycar race.)

I meant *HANS* with an unconscious driver.

HANS integrates with the belts system, and I've learned from (painful) experience that the belts tend to secure you more firmly when you're bracing yourself for the impact. So I wonder if HANS is still fully effective if the driver is already out cold before the impact.

I was thinking of KERS in terms of "a sh*tload" really being a true engineering term (first approximation) -- frequently used in connection with questions like, "What would it cost to develop a KERS system?".

 

You guys keep stating F=ma and then making assumptions based on that. "A" is acceleration and acceleration is velocity divided by time squared--again, many here have that right.

But what has gone unexplained is the acceleration that is appropriate. Appropriate acceleration is the acceleration of the projectile, not Massa's car. The projectile, as someone wrote earlier, was moving at about 120 MPH relative to Massa's head. The 120 MPH is a speed or velocity, not an acceleration. The acceleration in question is the negative acceleration (deceleration) of the spring from 120 MPH to something much less in a fraction of a second.

Here is another way to envision this. Assume your hand is outside your car window going 120 MPH and a golf ball hits it. It will break every bone in your hand.

 

The spring didn't accelerate. His head doing 120+ hit spring doing fraction of that. More like driving by post with same hand out window.

Distribution of the energy in an impact over a small area and a very short interval made for huge peak forces. Spring, skull and helmet cannot exist in same point in space, so something gives. Skull loses.

F=ma, but Ftot=[mass (head+ helmet)*accel]+[mass spring*accel]
Spring and helmet can dissipate energy by coming apart, bouncing away. Skull can only crush, brain is in enclosed space. Peak impact dissipated a little by skull, likely contre-coup fx (?basilar reported) and helmet, but brain still has velocity and acceleration. It also had 2nd deceleration with barrier, but far less peak force, car really not even deformed much.

The spike in force is the issue. Acceleration doesn't kill anyone. Sudden decceleration does.